The present invention relates to a button hole sewing device with a mechanism to be set on the sewing material and taken along by the latter and with control means for controlling the sewing process on the base of the movement of the mechanism. In this meaning, presser feet are more particularly known having slide like ground plates which are taken along together with the sewing material during the button hole sewing process and which are provided with marks in order to indicate the beginning and the end of the button hole sewing process. In this connection it is also known to sense by optical means the initial and the end position, respectively the intermediate or reversing position of the mobile ground plate which determines the length of the button hole, these optical means delivering corresponding signals to an electronic circuit which releases the corresponding control process (U.S. Pat. No. 4,216,732 U.S. Pat. No. 4,242,976).
In the place of slides which are taken along by the sensing material it is also known to use measuring wheels to be put on the sewing material and which comprise position encoders with optical sensor means e.g. reflectors in order to mark the initial and the end position (U.S. Pat. No. 3,596,618, U.S. Pat. No. 4,019,449). It is difficult in this case to associate with precision the beginning and the end of the sewing operation to the beginning and the end of the positions optically sensed.